We have constructed a physical map of polyoma viral DNA using a bacterial restriction enzyme from Hemophilus aegyptius. We propose to map the positions of various temperature-sensitive mutations and to use the radiolabeled fragments which contain these mutations as specific hybridization probes for polyoma genes and polyoma RNA in polyoma induced tumor cells. We propose to study also the configuration of the integrated viral genome in these cells as a means of studying the mechanism of integration and of gene regulation. We are studying the transcriptional regulation of the integrated genes of an RNA tumor virus in chromatin from uninfected chicken cells. We will investigate the influence of the structure of the integrated genes and the proteins bound to these genes on their availability for transcription by Escherichia coli RNA polymerase.